This invention relates to the field of active filters and, more particularly, to filter design using current mode operation, a minimum of components and supply voltage, and which is particularly suited to IC implementation.
In the past, most biquadratic active RC filter designs have used voltage mode operation with a relatively large number of components. The use of these filters in integrated circuit form has been limited by filter frequency variations due to the large tolerances on IC resistor and capacitor values, and by Q-enhancement or oscillation at high frequencies. These tolerances necessitate filter tuning if filter frequency is critical. The performance of many existing filter circuits would be degraded in an IC implementation due to the need for ungrounded capacitors. As is known in IC design, any capacitor not connected to either real or AC ground will be accompanied by a parasitic capacitor. Some previous designs have also required differential inputs which usually require additional components.